Module pool 

A pool of worker threads that lives as long as the backend, from spec/10-cpu.md.

Pool::run hands out tasks 0..n through a shared counter to the calling thread and every worker, and returns when all of them are done. Between jobs a worker spins for a while, since the next op of a plan is usually microseconds away, and then sleeps on a condition variable so an idle server costs nothing. A job is a borrowed closure, so running one allocates nothing.

Which thread runs a task depends on timing, but what a task computes does not, and that is what keeps results independent of the thread count.

Structs

Pool

Worker threads, created once.